Lifting magnet



Dec. 20, 1 93s. -H E H D SON- 2,140,700

LIFTING MAGNET Filed Oct. 25, 1935 9 o 1 a s 19 & 19 1? f 1? Patented Dec. 20, 1938 UNITED STATES PATENT OFFiilEi LIFTIN G MAGNET Application October 25, 1935, Serial No. 46,675

5 Claims.

This invention relates to lifting magnets, and more particularly to magnets for handling material such as coiled strip steel.

Lifting magnets are usually provided with an annular energizing winding which is carried by a circular magnet frame having an outer pole projection which surrounds the winding, and an inner pole projection located within the same. The pole projections are usually provided with removable pole shoes having an annular air gap therebetween and upon energization of the magnet the magnetic lines of force extend substantialy radially across such gap. While lifting magnets of this type may be advantageously employed in handling a wide variety of magnetic materials the same do not function properly when used to lift coiled strip steel.

In lifting coiled strip steel all part of the coil must be securely held to prevent slippage of any of the turns or otherwise the surface of the strip is likely to be marred or scratched. However, it has been found that when magnets of the character above described are employed for lifting material of this type the holding force on the turns of the coil which are located in the air gap between the pole shoes is relatively weak since it is necessary for the lines of force to pass through the various air gaps between such turns. Also due to the air gaps between such turns, the reluctance of the magnetic circuit of the magnet is relatively high and the total lifting force thereof is thus greatly reduced.

The present invention has among its objects to provide a new and improved lifting magnet which is particularly adapted for lifting coiled strip steel.

Another object is to provide a single coil magnet for lifting coiled strip steel having pole faces arranged to cause the lines of force of the magnet to pass substantially longitudinally through the several turns of such material.

Various other objects and advantages of the invention will hereinafter appear.

The accompanying drawing illustrates an embodiment of the invention which will now be described, it being understood that the embodiment illustrated is susceptible of modification without departing from the spirit and scope of the appended claims.

In the drawing,

Figure 1 is a vertical sectional View of a lifting magnet embodying the invention;

Fig. 2 is a bottom View of the magnet shown in Fig. 1;

Fig. 3 is a fragmentary vertical sectional view of the magnet taken at substantially right angles to the section shown in Fig. 1;

Fig. 4 is a perspective View illustrating the type of material which the magnet is designed to lift, and

Fig. 5 is a fragmentary bottom view illustrating the action of the magnet when the same is used to lift the material shown in Fig. 4.

The lifting magnet illustrated comprises a cir-- cular magnet frame I having a center pole projection 2 and an annular outer pole projection 3 on the under side thereof. A coil unit d is mounted in the space between said pole projections and said coil unit is supported by a coil shield 5 which is secured to magnet frame I by pole shoes 6 and I.

The coil unit 4 comprises a plurality of windings 8 formed of strap copper and. insulated in the usual manner, a cylindrical magnetic core Si bored to receive the center pole projection 2 and an annular magnetic plate I6 secured to the upper end of said core. The magnet is provided with the usual leads II which are connected to the windings 8 within a housing I2 on the upper face of magnet frame I and said magnet frame also has its upper face provided with the usual suspension lugs, one of which is illustrated at I 3. Pole shoe 6 is secured to magnet frame 2 by bolts I4 passing through openings in center pole projection 2 and having their heads countersunk in the lower face of said shoe. Said pole shoe has its upper face shouldered to fit within a counterbore I5 in the lower face of pole projection 2, and is shaped to provide an elongated substantially elliptical pole face I6 having end portions located below opposite sides of the outer pole projection 3.

Pole shoe 1 is secured to an outwardly projecting flange I! on the lower end of pole projection 3 by bolts I8 passing through openings in said flange and having their heads countersunk in the lower face of said pole shoe. Said pole shoe has a peripheral flange I9 on the upper side thereof which surrounds the flange I! on pole projection 3, and has projections 261-40 on the under side thereof having pole faces 2I-2I which are flush with the pole face I 6 of pole shoe 6. As shown in Fig. 2, the projections 20-20 are arranged on opposite sides of pole shoe 6 and are shaped to provide air gaps of substantially uniform width be tween the same and. the opposite sides of said latter pole shoe. Also as shown in Fig. 3 the end portions of pole shoe 6 are tapered to provide air gaps between said portions and the adjacent portions of pole shoe 1.

Fig. 4 illustrates a coil of strip steel which the Cir aforedescribed magnet is designed to lift. As now manufactured such coils are as wide as 96 inches and weigh as much as 23,000 pounds. For lifting such material the above described magnet is applied to one of the end faces of the coil in substantially centered relation with respect thereto, and the same is of sufiicient diameter to overlap all of the turns of the coil.

Referring now to Fig. 5, the same illustrates the action of the magnet when lifting a coil of strip steel. It should be noted that the pole face iii of shoe 6 overlaps each turn of the coil at points on opposite sides thereof and that the pole faces 2|2l of pole shoe 1 overlap a relatively large number of turns of the coil at points on opposite sides of pole shoe 8. Thus substantially all of the turns of the coil provide closed magnetic circuits from points at opposite ends of pole face IE to the pole faces 2l-2i. As a result, the lines of force of the magnet in crossing the air gaps between pole face l6 and pole faces 2l2i pass substantially longitudinally through the various turns of the coil as indicated by arrows in Fig. 5 and the various turns of the coil are thus securely held against slippage.

What I claim as new and desire to secure by Letters Patent is:

1. In a lifting magnet, in combination, a magnet frame having spaced inner and outer pole projections and an annular energizing winding mounted in the space between said pole projections, said inner pole projection having a single substantially oblong pole face diametrally disposed with respect to said winding and extending across substantially the entire face of said magnet frame and said outer pole projection having two elongated pole faces arranged on opposite sides of said former pole face and spaced with respect thereto to provide two elongated open magnetic gaps.

2. In a lifting magnet, in combination, an annular magnet winding, a circular magnet frame having inner and outer pole projections on the lower face thereof and an annular recess there between for receiving said winding and a plurality of pole shoes secured to said pole projections, said pole shoes being shaped to provide two open magnetic gaps which extend substantially in the same general direction across the entire face of said magnet frame and on opposite sides of said inner pole projection.

3. In a lifting magnet, in combination, an annular magnet winding, a circular magnet frame having inner and outer pole projections on the lower face thereof and an annular recess there between for receiving said winding, a single elongated pole shoe secured to said inner pole projection and having a substantially oblong pole face diametrally disposed with respect to said winding and extending substantially across the entire face of said magnet frame, and a pole shoe secured to said outer pole projection having elongated pole faces disposed on opposite sides of the pole face of said former pole shoe and spaced with respect thereto to provide two elongated open magnetic gaps on opposite sides of said inner pole projection.

4. In a magnet for lifting coiled steel strip, in combination, an annular magnet winding, a circular magnet frame having a downwardly projecting center pole located within said winding and a downwardly projecting outer pole of annular form surrounding said winding, said inner pole projection having a single elongated pole face diametrally disposed with respect to said winding and extending substantially across the entire face of said magnet frame to engage substantially all of the turns of the coiled strip steel at points on opposite sides of the axis of the latter and said outer pole projection having elongated pole faces disposed on opposite sides of said former pole face and spaced with respect to the latter to provide two elongated open magnetic gaps, each of said latter pole faces being also arranged to engage substantially all of the turns of the coiled steel strip.

5. In a magnet for lifting coiled steel strip, in combination, an annular magnet winding, a circular magnet frame having a downwardly projecting center pole located within said winding and a downwardly projecting outer pole of annular form surrounding said winding, said center pole having a single elongated pole face dia metrally disposed with respect to said magnet frame and extending substantially across the entire face thereof, and said outer pole projection having two elongated pole faces located on opposite sides of said former pole face and spaced with respect thereto to provide two elongated open magnetic gaps which are arranged to cause passage of substantially the entire flux of the magnet longitudinally through all turns of the coiled steel strip.

HOWARD E. HODGSON. 

